In recent years, to improve the appearance and visibility of optical articles, there has been a growing demand for a way to minimize smudging on the surface of such articles and a way to facilitate the removal of smudges. Because touch panel displays in particular are easily contaminated on the surface by skin oils, a water/oil repelling layer is generally provided thereon. The practice to date has been to use a protective glass or protective film to protect glass equipped with a touch sensor or film equipped with a touch sensor, and to provide a water/oil repelling layer on the surface of the protective glass or film. Recently, members having a water/oil-repelling function on the front side and a touch sensor function on the back side have been developed. Such members are obtained by mounting touch sensors on the back side of toughened glass, then water/oil-repellency treating the front side. However, for reasons having to do with production efficiency, there is a desire to first subject one side to water/oil-repelling treatment, and subsequently mount the touch sensors. A problem with this approach is that the water/oil-repellent layer has a poor heat resistance and is unable to withstand the high-temperature process of mounting the touch sensors.
From the standpoint of scuff and scratch resistance and fingerprint wipeability, preferred use is made of fluorooxyalkylene group-containing polymer-modified silanes as the water/oil-repellent layer on the surface of touch panel displays. A cover glass or cover film is generally provided on the surface of a touch panel display, although cover glasses or films integral to touch sensors have recently been developed. Their production appears to involve two types of processes: methods in which the touch sensor is mounted on a substrate, following which the substrate is water/oil-repellency treated on the back side, and methods in which a touch sensor is mounted on the back side of a substrate that has already been water/oil-repellency treated. In the latter case, the water/oil-repellent layer must be able to withstand the heating step during mounting of the touch sensor.
Also, when a water/oil-repellent layer is provided as a mold release layer for thermal imprinting, it is essential that it withstand the heating temperature during processing. In cases where fluorooxyalkylene group-containing surface treatments have been used as a mold release layer in applications such as thermal imprinting, although such treatments have excellent mold release properties, owing to their poor heat resistance, they have been unable to withstand high-temperature processes.
Fluorooxyalkylene group-containing compounds have a very low surface free energy, and so generally possess such attributes as water and oil repellency, chemical resistance, lubricity, mold release properties and anti-smudging properties. These qualities are widely used industrially in, for example, water/oil-repellent stain-proofing agents for paper and textiles, lubricants for magnetic recording media, oil-proofing agents for precision machinery, mold release agents, cosmetics, and protective films. At the same time, these qualities also manifest as non-tackiness and non-adherence to other substrates. Thus, even when such a compound can be coated onto a substrate surface, having the coat adhere to the substrate has been difficult.
Of related interest here are silane coupling agents, which are familiar as materials that bond together substrate surfaces such as glass or fabric with organic compounds, and are widely used as coating agents for various types of substrate surfaces. Silane coupling agents have an organic functional group and a reactive silyl group (particularly a hydrolyzable silyl group) on a single molecule. The hydrolyzable group gives rise to a self-condensing reaction due in part to moisture in the air, forming a coat. In this coat, the hydrolyzable silyl groups bond chemically and physically with the surface of the glass, fabric or the like, resulting in a strong and durable coat.
Articles that have been surface-treated in the above manner are rarely used at elevated temperatures of 250° C. and up, and so heat resistance to 250° C. or more has not often been called for in water/oil-repellent layers. However, when touch sensors are to be mounted on the back side of water/oil-repellency treated substrates, and when water/oil repellent treatment agents are used as mold release agents in thermal imprinting, exposure to elevated temperatures sometimes occurs. In such cases, there is a need for the water and oil repellency, wear resistance and mold release properties to be retained even after the treated substrate has passed through a heating step.
The inventors earlier proposed, in JP-A 2012-072272, a fluorooxyalkylene group-containing silane of the formula shown below. Glass treated with this fluorooxyalkylene group-containing silane has, in particular, outstanding slip properties and excellent abrasion resistance. However, when this treated glass is exposed for one hour at a temperature of 250° C. or more, a satisfactory performance cannot always be obtained.
In the formula, Rf is —(CF2)d—(OC2F4)e(OCF2)f—O(CF2)d—, A is a monovalent fluorine-containing group with a —CF3 group at the end, Q is a divalent organic group, Z is an organopolysiloxane residue with a valence of 2 to 8 and having siloxane bonds, R is an alkyl group of 1 to 4 carbon atoms or a phenyl group, X is a hydrolyzable group, a is 2 or 3, b is an integer from 1 to 6, c is an integer from 1 to 5, α is 0 or 1, each d is independently 0 or an integer from 1 to 5, e is an integer from 0 to 80 and f is an integer from 0 to 80, with the proviso that the sum e+f is an integer from 5 to 100, and the repeating units may be randomly bonded.
It is therefore an object of this invention to provide a water/oil repellent treatment agent that is able to form a water/oil-repellent layer which, even after being heated at an elevated temperature of 250° C. or more, retains excellent water/oil repellency, abrasion resistance and mold release properties. Further objects of the invention are to provide a method for preparing the water/oil repellent treatment agent, and to provide an article treated therewith.